TXU0304-Q1: Any issues connecting output/A4Y of two TXU0304-Q1 together?

Mark Feller

Part Number: TXU0304-Q1
Other Parts Discussed in Thread: TXU0304

Are there any issues with connecting the output (for example, A4Y) of TXU0304-Q1 together?

In the design that I am looking at, there are two SPI devices that we want to interface to one MCU. MISO from each SPI device would be connected to B4 of one TXU0304. Only one of the SPI devices would be driving MISO/B4 at one time. So you have a situation where "device 1" might have MISO/B4 high, "device 2" would have MISO/B4 low. Are there any issues at A4Y? Attempting to draw it...

Thanks!

5 months ago

+1 Michael Ikwuyum 5 months ago

TI__Mastermind 26790 points

Hi Mark,

Yes, two outputs shorted together can cause damage if there is an external bus contention that drives one output high and the other low, thanks.

Best Regards,

Michael.

0 Mark Feller 5 months ago in reply to Michael Ikwuyum

Intellectual 900 points

Thanks for the quick response.

0 Mark Feller 5 months ago in reply to Michael Ikwuyum

Intellectual 900 points

Also, outside of causing damage, do you have any guess as to what the behavior will be? For example, if device 1 has output 5V on B4, and device 2 has output 0V on B4, VCCA is 3.3V, I see 1V at A4Y.

0 Mark Feller 5 months ago in reply to Michael Ikwuyum

Intellectual 900 points

Sorry, one more question: I found this thread : https://e2e.ti.com/support/logic-group/logic/f/logic-forum/1120917/txu0304-connect-multiple-txu0304-two-different-spi

where it seems like the configuration in my example is okay, based on feedback in that thread. Can you reconfirm if "option 2" in the attached is okay, if the MISO-LV from each slave is different (one 3.3V, one 0V)?

+1 Clemens Ladisch 5 months ago in reply to Mark Feller

Guru 263860 points

When there is bus contention, the resulting voltage depends on the drive strength of the two outputs. In theory, it's the same and you get V_CC/2; in practice, there might be differences in the short-circuit current. In any case, the voltage is likely to be invalid.

The linked thread is not correct; only the first option would work.

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TXU0304-Q1: Any issues connecting output/A4Y of two TXU0304-Q1 together?